1. Field of the Invention
The present invention relates to overvoltage protection technology and more particularly, to an overvoltage protection device made by: making at least one through hole on a substrate, and then filling an overvoltage protection material in each through hole, and then employing a metallization technique to form a flat electrode on the top and bottom sides of the overvoltage protection material in each through hole.
2. Description of the Related Art
Regular electronic products and their related peripheral devices use many active and passive components. An active (microprocessor or chip) can perform operation and data processing independently. A passive component does not require electrical power to operate and is not capable of power gain. Capacitor, resistor and inductor are the three major passive components intensively used in information, communication and consumer electronics as well as many other industrial products to constitute an electronic control loop.
However, abnormal high voltage and static electricity are harmful to electronic devices and difficult to be eliminated. When an electronic product receives an abnormal high voltage or electrostatic discharge, an unstable condition, such as function failure, may occur. When this problem occurs, the user may have to reset the system, or the internal components may be damaged by the abnormal high voltage or electrostatic discharge. To avoid this problem, an overvoltage protection device may be used. An overvoltage protection device is a passive component intensively used in cell phone, motherboard, notebook computer, digital camera and etc. to protect the internal electronic components of the electronic product against any abnormal high voltage and electrostatic discharge, for example, to protect the LED of a backlight module of an electronic product against abnormal high voltage and electrostatic discharge.
Further, in a conventional LED device, LED chips are installed in a cooling substrate, and gold or aluminum wires are bonded to electrically connect the electrodes of the LED chips to positive and negative electrodes of the cooling substrate, and overvoltage protection device, for example, Zener diode are bonded to the cooling substrate by means of SMT or flip-chip technology. Alternatively, low-temperature cofired ceramics may be directly formed in the surface of the cooling substrate, and then gold or aluminum wires are bonded to electrically couple the overvoltage devices to positive and negative electrodes of the cooling substrate for enabling the overvoltage protection devices to protect the LED chips against abnormal high voltage and electrostatic discharge.
The aforesaid method of coupling Zener diodes in parallel to LED chips to form an overvoltage protection loop can effectively protect the LED chips against abnormal high voltage and electrostatic discharge. However a LED product of this design does not allow positioning of the optical axis at the center. A certain area of the cooling substrate must be left for the installation of the overvoltage protection devices, shortening the effective reflective area, lowering the light extraction and heat dissipation efficiency and complicating optical axis design. If aluminum nitride, high purity aluminum oxide or other high conductivity material is used, or a crystal-pulling technique is employed, a vacuum or reduction sintering process is necessary to sinter the material at a high temperature (1600˜1700° C.). It is difficult and expensive to make an embedded overvoltage protective device under this high temperature condition.
Therefore, there is a strong demand to provide an overvoltage protection device fabrication method for making an overvoltage protection device for LED product by embedding a high thermal conductivity type overvoltage protection material in a cooling substrate that effectively protects the LED chips against overvoltage and electrostatic discharge, keeps the surface of the substrate smooth, allows free arrangement of the LED chips to keep the optical axis at the center of the substrate, and improves light extraction and heat dissipation efficiency.